Why Your Cat's Tongue Is Nature's Perfect Hairbrush

A lick from a cat is a mixed blessing. On the one hand, cats don’t dole out affection to just anyone, so it’s a true compliment when they try to groom you. On the other hand, their tongues feel like sandpaper wrapped in barbed wire. Those sharp tongues are actually incredible tools, according to a new study published in Proceedings of the National Academy of Sciences. Their unique structure is very efficient at depositing saliva on cats' fur to help them clean themselves and keep cool. Researchers from Georgia Tech made the discovery using high-speed video, CT scans, and “grooming force measurements.”

Cats aren't just prettying themselves up when they spend all day grooming themselves, the study shows. (That’s not an exaggeration—house cats can spend up to a quarter of their waking lives grooming.) As they lick themselves, their tongues remove debris, fleas, and excess heat from their fur thanks to those sharp, curved spines—called filiform papillae—that are so unpleasant to feel on your skin.

These keratin-based filiform papillae have U-shaped hollows at their tips that allow cats to wick saliva from their mouths onto their fur, helping them regulate body temperature and cool down. Each of these papillae can carry one-tenth of an eyedropper’s worth of spit, half of which gets deposited on the fur. The papillae spread the saliva along the roots of each hair, allowing it to penetrate cats’ fur so that it can cool their skin. Saliva alone can provide 25 percent of a cat’s cooling needs, according to the study.

This useful adaptation isn’t limited to domestic cats. Researchers looked at tongue tissue from six different species—bobcat, cougar, snow leopard, tiger, and lion, in addition to house cats—and found similar structures.

As part of the study, the researchers also created a flexible “tongue-inspired grooming" (TIGR) brush with the help of 3D models of a house cat’s papillae. They found it was easier to clean than a typical human hairbrush—hair could be removed from it in one swipe, without the tweezers or other tools you need to get hair out of the stiff bristles of the typical hairbrush. (The wavy ridges on the roofs of cats’ mouths may do this job in the animals themselves.)

The brush has several potential uses. Because of its papillae-inspired structure, it could be used to apply liquids to cats’ skin. That could be helpful for applying topical medication, but it might also be a way to wash off some of the allergens they produce that bother humans. Potentially, there could be human uses for a papillae-like hairbrush in the future, too. You could imagine using it to brush styling products evenly through your hair, for instance. The researchers suggest the structure "may provide inspiration to soft robotics and biologically inspired technologies for sorting, cleaning, and depositing fluids into fur and arrays of flexible filaments."